A difficult obstacle associated with the exploration and production of oil and gas is management of significant ocean currents. These currents can produce vortex-induced vibration (VIV) and/or large deflections of tubulars associated with drilling and production. VIV can cause substantial fatigue damage to the tubular or cause suspension of drilling due to increased deflections.
One solution is to install helical strakes onto the tubular. Typically, helical strakes are made by installing fins helically around a cylindrical shell. The cylindrical shell may be separated into two halves and positioned around the tubular to helically arrange the fins around the underlying tubular. Helical strakes, if properly designed, can reduce the VIV fatigue damage rate of a tubular in an ocean current.
There are some important installation issues and challenges associated with helical strakes. Surface installation requires human intervention to mechanically install the helical strake sections around the tubular. This installation can be time consuming and expensive, since the daily cost of installation vessels are quite high.
Installation of helical strakes in the ocean can be both difficult and extremely expensive. It is critical that high precision be present in the strake design so that opposite sides of the helical strake align properly when attaching a helical strake section around a tubular.
Another issue with helical strakes is the thermal and electrical insulation that they impart onto a tubular. Sometimes helical strakes having fins attached to a cylindrical shell provide more thermal insulation around the tubular than desired. Other times, helical strakes impede cathodic protection systems.